* Allow more types to be converted to throw_error::Error
## Context
At the moment it is quite difficult to get crates like `anyhow` to play
well with leptos, in particular because it is _very_ difficult to
convert an `anyhow::Error` type to a `leptos::Error` type. This is
because the only way to construct a `leptos::Error` currently is via its
`From` implementation, which exists for any type that implements the
standard `Error` trait, but `anyhow::Error` does not implement
`StdError` directly. It can however be converted to a boxed trait object
via its [`.into_boxed_dyn_error()`][4] method, and you would think that `Box<dyn
Error>` implements `Error`, but [that is sadly not the case][1].
## Solution
Change the blanket implementation of `From` for `throw_error::Error`
from "any type that implements the Error trait" to "any type that can be
converted to a boxed Error trait object".
This works because:
- A `Box` [can be converted][2] to an `Arc` for any type (including unsized
types like trait objects),
- Any type that implements the standard `Error` trait [can be
converted][3] to a `Box<dyn Error>`, so the new `From` blanket
implementation covers a strict superset of what was previously
allowed.
This change now allows types like `anyhow::Error`, but also `String`, to
be easily converted to a leptos `Error`, therefore making them play well
with things like `<ErrorBoundary>`.
[1]: https://stackoverflow.com/questions/65151237/why-doesnt-boxdyn-error-implement-error
[2]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#impl-From%3CBox%3CT,+A%3E%3E-for-Arc%3CT,+A%3E
[3]: https://doc.rust-lang.org/stable/std/error/trait.Error.html#impl-From%3CE%3E-for-Box%3Cdyn+Error%3E
[4]: https://docs.rs/anyhow/latest/anyhow/struct.Error.html#method.into_boxed_dyn_error
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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
